ultraviolet germicidal light · Mar 24, 2022

UltraViolet (UV) energy: what is this weapon of mass sanitation?

If you think about it, UV energy is really quite a powerhouse weapon. Everywhere things are exposed to sunlight, certain germs are dying. It also would kill us in a slow way, if we aren’t careful. Some of the best benefits of research have been on how to use UV energy for our health.

Ultraviolet "light" is just beyond the range of visible light (violet) with the shortest wavelength. This is on the opposite end of red light. Shorter wavelength = more energy, hence it is energy that can harm life. If you keep going in the shorter wavelength direction, you will encounter x-rays and gamma rays (radiation).

Graph source: waveformlighting.com

UV energy has been in use since the mid-1900’s for sanitation purposes, starting with drinking water facilities and then moving into disinfection of medical facilities and instruments. Here are some terms in this field:

nm (nanometer, a billionth of a meter), used to measure wavelength
UV-C: 100-280 nm, the wavelength range of germicidal UV lights, not naturally found at the earth’s surface atmosphere
UV-B: 280-315 nm, found in natural daylight
UV-A: 315-400 nm, found in natural daylight
UVGI (UltraViolet Germicidal Irradiation): this type of UV light is in the shorter wavelengths of the whole UV range, between 200 and 300 nanometer (nm, a billionth of a meter) wavelength.

As you can see from the above graphic, UV-C doesn’t naturally appear at the earth’s surface, because ozone in the earth’s atmosphere absorbs it. UV-A and -B rays are much more common as they are found in sunlight and used in beneficial purposes such as curing and fluorescence applications.

Traditionally, UV-C is used in germicidal applications because DNA and RNA are susceptible to damage by energy at around 265 nm. The damage is called dimerization, the breaking of specific bonds found in the pathogen’s genomes (waveformlighting.com). Damage to human cells is usually quickly repaired by the DNA’s own repair mechanisms, but sometimes it is not; this type of photochemical damage, called pyrimidine dimers, is the primary cause of melanoma. (wikipedia) Because of the risk of this type of energy damage to humans, the American Conference of Governmental Industrial Hygienists (ACGIH) has issued Threshold Limit Values (TLVs) for occupational exposure to UV radiation. These thresholds are based on the irradiance (measurement of energy per unit area in a specific wavelength range) and time of exposure. Since imposing these limits in 1972, they have hardly been changed since then, because relatively few workers (mainly welders and scientists) are exposed to this type of energy on a regular basis. (study) However, the need to sanitize larger areas due to the COVID pandemic, and research into what wavelengths, irradiance and time of exposure most effectively kill the SARS-CoV-2 virus, may change what wavelengths to be “dangerous”.

Bridges, like wine glasses, cannot vibrate in certain frequencies for very long before they “self-destruct” (as in this video). Similarly, new research is determining which UV frequencies are safe to our DNA while being fatal to viruses, in order to allow people to safely co-exist with UV lights in germicidal frequencies for longer periods of time:

Inactivation (inhibiting ability to infect) of viruses like SARS-CoV-2 by UV radiation depends on the wavelength, amount of energy, and time of exposure.

Traditional UV systems use wavelengths at or around 254 nanometers. At these wavelengths the light is dangerous to human skin and eyes, even at low doses.
Skin cells can tolerate shorter wavelengths than eye cells, because the outer layers of skin “shield” the deeper layers that are most sensitive to UV radiation damage. The layer of tears around our eyes also works to block out germicidal UV rays.
New research shows that at wavelengths of 230 nm or less, lower doses of UV light do not damage skin or eyes, yet are able to deactivate the SARS-CoV-2 virus. Specifically, systems that apply energy at the 222 nm wavelength require the lowest dose of energy to inactivate the virus. These doses could allow people to be in the same space without damage to their eyes or skin, for up to 1 hour 20 minutes. Another study using this same wavelength (222 nm) showed a 98% reduction in aerosolized Staphylococcus aureus that was released into a 32 m3 chamber in less than five minutes with a high dose of the light. Ninety-two percent reduction of the bacteria was accomplished with a medium dose of the light in less than 15 minutes, showing that using far-UVC is as effective as increasing baseline ventilation rate by 11 times!

If this research is adopted into higher threshold limits, we could see 222 nm systems installed in malls, restaurants and other public spaces in the future. Until then, here is what and how can we sanitize at home with UV light:

Masks and frequently used items like keys and sunglasses can be conveniently placed in boxes like this, which use 254 nm light.
CrazyCap is a brand that makes self-cleaning water bottles, which are perfect for hikers and those who really don’t clean them as often as they should (just about everyone?). It has a UV light fitted into the cap that sanitizes the contents of the bottle.
Keep the clean going continuously with these hidden UV-C sanitizers. By placing or aiming them out of contact with skin or eyes, the UV radiation will not contact humans as we work or play nearby.
- Air Angel is our small, portable sanitizer that draws air in through and radiates it with a UVGI lamp.
- Ceiling fans like the Ultra or Haiku incorporate UV-C into the top of the fan motor and aiming it at the ceiling, so that it radiates the air between the fan and ceiling, while the fan constantly circulates air in the room.
- In-duct UVGI works in the safety of your HVAC furnace or ducting so that whenever the fan is on, the light will irradiate passing air to quickly sanitize the air in your whole home. Here is a great list of in-duct UVGI lights.

Sunscreen and sunglasses are still prescribed when going outside, but hopefully we can safely play under UV light inside sometime soon!

Photo by Serge Kutuzov on Unsplash

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